An alternating current to direct current (AC-to-DC) power supply is widely used to convert an alternating current (AC) voltage to a direct current (DC) voltage to provide power to a load. As illustrated in FIG. 1, a prior art power supply includes a rectifier and a bulk capacitor for energy storage. The rectifier rectifies an AC voltage received from an AC power source into a rectified DC voltage. The bulk capacitor receives and filters the rectified voltage to produce a DC voltage with reduced ripple and provides the DC voltage to a load.
The DC voltage provided to the load may need to stay in regulation for a certain amount of time after the AC power source is removed or fails. The amount of time the power supply continues to regulate after the AC power source is removed is referred to as hold-up time. During the hold-up time, the bulk capacitor operates to provide the necessary temporary power for the load as it discharges. In most AC-to-DC power supplies the minimum hold-up time is required to be the time necessary to maintain voltage regulation for at least one missing AC cycle of the AC power source.
In order to provide a desired DC voltage in different countries, the AC-to-DC power supplies are configured to operate for a wide range of AC input voltage. The volume of the bulk capacitor is influenced by the value and the voltage rating of the bulk capacitor. Therefore, bulk capacitors having a large volume are needed due to the high capacitance values demanded by the minimum AC input voltage combined with very high voltage ratings demanded by the maximum AC input voltage. Not only is the size of such bulk capacitors large, their cost is also relatively high. Since a physical size and a cost of the power supply are strongly influenced by the cost and size of the bulk capacitor, the conventional power supply is bulky in size and also costly.